The Analytical Electron Microscopy Facility in the Division of physiology, Department of Cell Biology, Duke University School of Medicine, is one of fewer than a dozen such laboratories in the world using quantitative x-ray microanalysis and imaging to examine correlative structural-functional aspects of ionic homeostasis and subcellular compartmentation. The Facility has grown since its organization in 1982 to serve more than seventeen Faculty members in the Duke Department of Cell Biology, Pathology, Neurobiology, Physics and Medicine, Research Triangle Institute, the University of North Carolina at Chapel Hill, and Harvard university. To meet the scientific needs and enhance the expanded scope of research endeavors of the major users, the Facility must acquire a second, permanent state-of-the art analytical electron microscope. Funds are requested to purchase the JEM100CX-II TEMSCAN, currently on consignment in the Facility, and to upgrade this microscope with accessories for performing quantitative high resolution x-ray microanalysis and imaging. The goals of the Facility are (1) to acquire analytical instrumentation for (a) quantitative x-ray mapping of elements (Na, P, S, Cl, K, Ca), (b) electron energy loss measurement of intracellular water content, and (c) high resolution immunolocalization and quantitative mapping of cell proteins; and [2] to apply the techniques thus available to (a) assess the role of Ca compartmentation in renal cell injury; (b) explore the role of element-rich intracellular vacuoles in the metabolism of a clinically important protozoan, leishmania major (c) elucidate the mechanisms that maintain ionic homeostasis in cultured cardiac cells; (d) characterize elemental compartmentation in cystic fibrosis epithelia; (e) clarify the role of structural damage in altering ionic compartmentation and homeostatic mechanisms during irreversible cardiac cell damage; (f) antigenically label and quantitatively map Na-pump sites in lingual epithelia; (g) determine the time course of release of Ca from storage sites in skeletal muscle; and (h) examine the role which calciosomes play in pancreatic cell Ca regulation. An organizational plan for Facility operation has been in place for eight years and, under the direction of the established internal advisory committee, will function to provide all users with technical expertise and equitable access to instrumentation. A substantial institutional commitment to the growth and development of the Facility is reflected in a financial contribution towards the cost of the instrument. The multiuser, multidisciplinary nature of the Facility insures that this costly instrumentation will be used to full potential and capacity. In summary, a versatile state-of-the art analytical electron microscope will fulfill urgent instrumentation needs of a growing number of users in Duke Medical Center who wish to determine how structural and ionic compartmentation relates to the mechanisms involved in maintaining intracellular ionic homeostasis in both health and disease. The continued development of these advanced microanalytical and microstructural imaging techniques, and their application to fundamental and applied problems in cell biology, physiology and pathophysiology, will benefit not only Duke University but also the overall biomedical and bioengineering community.